I was curious, where are the pros and cons of both, for providers specifically. For hobbyists, I can only assume that the majority here prefer indies since you are doing the research.
Typically from what I can tell as a client some pros are:
-agencies have multiple ladies available to choose from
-typically lower cost
-may be easier to book last minute
cons:
-typically the lower cost means higher volume which may mean rushed sessions
-bigger target for law enforcement
As a provider, I can only imagine the biggest benefit would be that you don't have to deal with scheduling as much. On the flip side, you may also lose control as to who you get to see. You do have to give the agency a cut. I can be mistaken on this, but I've heard the costs of the hotel can be covered by the agency and/or split between the agency or provider. You don't have to worry about doing screening as the agency typically takes care of that. However, some agencies may not do a very good job at screening which really puts everyone involved at risk.
Perhaps other providers might be able to share more information.
As a client, my preference is definitely indies. Particularly for me, its the two cons I mentioned that concern me the most. However, sometimes those agencies get some really beautiful providers and its hard to pass up. I guess for ladies agencies just make it so much easier and perhaps a little less daunting if they just want to score some bucks without all the overhead and hassle that comes with booking appointments. Some do eventually leave agencies though and go indie.
Agency take half of your money!
they expect you to see everyone they book for you or else they will fine you.
you do not get to pick your own schedule or stop working if you are not feeling good.
If you are just starting out, you can work for an agency for couple months but go independent after that when you feel comfortable doing the business on your own, advertise your own self and get Incall. 
Yes, and I mostly agree with loverileytaylor with her observation, depending on the stage of their providing companionship.
There are ladies who would go the agency route and would realize that they could command an audience of their own and would turn independent.
Most of the independent ladies that I have met have not turned agency.
LoveRileyTaylor is one of those beautiful ladies with whom I hope to meet soon, and our past schedules did not work out.
When I look back at the reviews that I have written and the companions with whom I have enjoyed the strongest connections, most of them happen to be independent when I met them, and quite a few have advanced degrees Master/PhD